SOLUTION: The monthly cost of water use is a linear function of the amount of water used is in HCF. The cost for using 19 HCF of water is $32.11, and the cost for using 55 HCF is $80.71. Wha

Algebra ->  Coordinate Systems and Linear Equations  -> Linear Equations and Systems Word Problems -> SOLUTION: The monthly cost of water use is a linear function of the amount of water used is in HCF. The cost for using 19 HCF of water is $32.11, and the cost for using 55 HCF is $80.71. Wha      Log On


   

Question 1124378: The monthly cost of water use is a linear function of the amount of water used is in HCF. The cost for using 19 HCF of water is $32.11, and the cost for using 55 HCF is $80.71. What is the cost for using 30 HCF of water?
Answer by josmiceli(19441) About Me  (Show Source):
You can put this solution on YOUR website!
Plot HCF on the horizontal axis
Plot cost on the vertical axis
Let +x+ = HCF
Let +c+ = cost
———————————————
Use point-slope formula to find equation
+%28+c+-+32.11+%29+%2F+%28+x+-+19+%29+=+%28+80.71+-+32.11+%29+%2F+%28+55+-+19+%29+
+%28+c+-+32.11+%29+%2F+%28+x+-+19+%29+=++48.6+%2F+36+
+%28+c+-+32.11+%29+%2F+%28+x+-+19+%29+=+1.35+
+c+-+32.11+=+1.35%2A%28+x+-+19+%29+
+c+-+32.11+=+1.35x+-+25.65+
+c+=+1.35x+%2B+6.46+
——————————————
Let +x+=+30+
+c+=+1.35%2A30+%2B+6.46+
+c+=+40.5+%2B+6.46+
+c+=+46.96+
The cost is $46.96
———————————
Check the equation:
+c+=+1.35x+%2B+6.46+
+32.11+=+1.35%2A19+%2B+6.46+
+32.11+=+25.65+%2B+6.46+
+32.11+=+32.11+
OK